Interstate 370

I-370 at MD 355, from top-left to center-right

I-370 begins a short distance to the west of the I-270 interchange in Gaithersburg, Montgomery County, heading northeast as a six-lane freeway. Southwest of this interchange, the road continues as Sam Eig Highway (named after Washington real estate developer Sam Eig)[2] which interchanges with Washingtonian Boulevard before becoming a surface road. The highway passes woods to the northwest and a shopping center to the southeast as it reaches an interchange with I-270. From this point, I-370 turns east and runs between residential neighborhoods to the north and business parks to the south, with trees separating the road from these areas. The freeway curves northeast again and comes to the MD 355 interchange. Past this, the highway passes more commercial development before reaching a bridge over CSX's Metropolitan Subdivision. A short distance later, I-370 comes to a trumpet interchange with MD 200A, a road that provides access to Shady Grove Road and the Shady Grove station of Washington Metro's Red Line. At this point, I-370 ends and the freeway continues east as MD 200 (Intercounty Connector).[1][3]

View east at the west end of I-370 at Sam Eig Highway in Gaithersburg

What is now I-370 was originally proposed as part of the Intercounty Connector in the late 1970s. The I-370 freeway opened on December 17, 1988, connecting I-270 to the Shady Grove Metro station.[4] After three and a half years of construction, the freeway was four lanes wide and 2.5 miles (4.0 km) long.[4] Its construction cost $169 million, with federal funds paying for ninety percent of the cost.[4] The state of Maryland's portion of the cost was funded with a portion of the proceeds of a nickel-per-gallon gas tax increase in 1987.[5] Prior to its opening, driving from I-270 to the Shady Grove Metro station involved exiting at Shady Grove Road and passing six traffic lights to arrive at the station.[4] Upon its opening, the remainder of the Intercounty Connector was planned but not yet built.[6] At the time, it was the third shortest interstate, after I-878 in New York and I-395 in Baltimore.[4]

In 2007, construction began on MD 200, which was to head east from I-370. At this time, the ramp from Shady Grove Road to westbound I-370 was shifted to a new alignment.[7] In 2009, the lanes along I-370 were shifted to allow for construction of the MD 200 interchange.[8] Construction on this segment of MD 200 was completed in February 2011, with the road opening to traffic on February 23.[9][10] As a result of the completion of MD 200, the eastern terminus of I-370 was truncated to the west end of MD 200, with the freeway connection to the Shady Grove Metro station becoming MD 200A.[11]

The entire route is in Montgomery County.

Location	mi[1]	km	Exit	Destinations	Notes
Gaithersburg	0.00	0.00	—	Sam Eig Highway to Fields Road	Continues west without designation to MD 119
	0.43	0.69	1	I-270 – Frederick, Washington	Signed as exits 1A (south) and 1B (north); no exit number eastbound; exit 9A on I-270
	1.15	1.85	—	Shady Grove Road to MD 355 south – Rockville	Eastbound exit only
	1.93	3.11	2	MD 355 (Frederick Road) – Gaithersburg, Rockville, Town Center	No eastbound access to MD 355 south; former US 240
Derwood	2.14– 2.36	3.44– 3.80	3	Shady Grove Road – Metro Station	Signed as exit 3A (Shady Grove Road) and 3B (Metro Station) eastbound; unsigned MD 200A; commercial vehicles cannot use exit 3B
	2.54	4.09	—	MD 200 Toll east to I-95	Continues east as MD 200 Toll (Intercounty Connector)
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Electronic toll collection

•  Maryland Roads portal

• Media related to Interstate 370 at Wikimedia Commons